How to Repoint a Brick Wall
Mix up enough mortar for 30 minutes’ use.
Slowly add water until the mix is stiff enough to form a ball. Then mound it up. The mix should stand without collapsing or slumping.
Mortar continues to stiffen as it sets; so, if you mix up too much mortar, you'll just end up throwing it out. At least you have a good excuse for working on the house a little at a time, as long as you do the worst areas first.